On A320 there are 3 ADIRU. ADIRU 1 is shown on Capt display, ADIRU 2 on F/O display. ADIRU 3 can be selected manually. The AoA value is not displayed by default, but it is accessible on the MCDU after selecting the related page. However the values are always used by computers.
Each ADIRU contains an air data reference (ADR) and an inertial reference unit (IRU). Each ADR receives the AoA value from a separate AoA probe.
If values from ADR disagree, pilot intervention is required and any ADR can be disconnected. From this report:
If one ADR has been detected as being faulty, or has been rejected by the flight control computers, and there is an airspeed or angle of attack disagreement between the remaining two ADRs, then a level 2 alert is raised. This activates the master caution and presents an amber NAV ADR DISAGREE message on the ECAM.
All pictures are from the report.